This application claims the priority of German Application No. 100 21 602.1, filed May 4, 2000, the disclosure of which is expressly incorporated by reference herein.
The invention relates to a method and apparatus for detecting a disconnection in the charge line between a Regenerator and an electric battery in a motor vehicle.
Motor vehicles, in particular those with a 12 V electric system, are provided with energy by means of a regulated three phase generator. For an understanding of the technical background of electronic generator regulators, see in particular the technical manual xe2x80x9cAutoelektrik, Autoelektronik am Ottomotorxe2x80x9d [Automotive Electrics, Automotive Electronics at the Otto Engine], BOSCH, VDI Verlag, 1994. The trend today in the development of electronic generator regulators is toward independent intelligent controllers, predominantly with a data connection line to other controllers, such as the internal combustion engine controller. Compared to past generator regulators, this trend makes it possible to increase the range of functions in the generator regulator. For example, to avoid erratic torque changes when applying current to large electric loads, the output power of the generator is adjusted upward to a predetermined generator speed according to a defined ramp (so-called load response function, cf. German Patent document DE 196 36 357 A1). Furthermore, other diagnostic and error detecting routines are provided.
Currently, a disconnection or open circuit in the charge line from the generator to the battery, such as an intermittent contact due to a loose connection, cannot be undetected. Hence, the generator does not detect an error, but rather merely assumes that the electric system does not need any current. Consequently, the excitation is reduced to a minimum, or is totally turned off for a period of time. If, in the case of a loose connection, the connection, is re-established temporarily, the generator detects a load and begins to adjust upwardly the generator output, for example in accordance with the load response function (LRF). Continuous repetition of this sequence results in permanent insufficient output of the generator and, finally, to a depletion of the charge level of the motor vehicle""s battery. This error situation can be reproduced only with difficulties in workshops and, therefore, leads to the unnecessary replacement of batteries and generators. The charge line from the generator output to the battery connection usually comprises a plurality of individual partial lines, assembled by means of plug connections or other connections. Therefore, the illustrated error is not rare.
The object of the invention is to improve error diagnosis in a generator regulator, in order to prevent unnecessary service and parts replacement costs.
This problem is solved by a process for detecting a disconnection in the charge line between a generator and an electric battery in a motor vehicle. The generator output voltage is measured and is evaluated at least with respect to the ripple voltage. A disconnection in the charge line is detected, when the ripple voltage has reached or exceeded a predetermined ripple threshold value. A device for carrying out the process for detecting a disconnection in the charge line between a generator and an electric battery in a motor vehicle includes a device, by which the generator output voltage is measured and is evaluated at least with respect to the ripple voltage, and a device, by which a disconnection in the charge line is detected, when the ripple voltage has reached or exceeded a predetermined ripple threshold value. Advantageous further developments of the invention are described herein.
According to the invention, a disconnection, for example in the form of a loose connection or in the form of a permanent disconnection, occurring in the charge line between a generator and an electric battery in a motor vehicle is detected when the ripple content of the generator output voltage or the ripple voltage has reached or exceeded preferably its mean value over a predetermined time span, a predetermined ripple threshold value, preferably after a predetermined or for a predetermined period of time (for example 2 ms). The ripple threshold (approx. greater than 3 V or raised by a factor of 2) can-be predetermined as a fixed number or can vary as a function of the generator speed and/or the generator current. The ripple content or the ripple voltage is the voltage value between a maximum and a minimum of the remaining fluctuations in the generator output voltage after rectifying the output voltage, generated by a three phase generator.
The invention is based on the knowledge that the ripple voltage for an intact charge line between the generator and the battery is very small, since the fluctuations can be smoothed out by means of a battery, acting like a capacitor. The battery does not exert any smoothing effect when the charge line is disconnected.
Preferably, a disconnection in the charge line is detected when the ripple voltage reaches or exceeds a predetermined ripple threshold, after the generator output voltage has reached or exceeded a predetermined load shedding threshold value (for example, 18 V in a 12 V electric system). This further development of the invention is based on the knowledge that the transition from an intact to a disconnected charge line in accordance with a load shedding results first in a voltage overshoot. Correspondingly, the inventive evaluation of the ripple voltage with respect to a ripple threshold does not talk place until this voltage overshoot has occurred. In this respect it must be noted in terms of circuit engineering that even just very short voltage overshoots (for example, for 0.1 ms) are detected. In this manner the error detection accuracy is raised.
Furthermore, a disconnection in the charge line is not inferred preferably until an error in the output stage for driving the exciting coil has been ruled out. Because in the case of an error in this output stage, especially in a conductively alloyed output stage, the generator generates over voltages (for example, up to 20 V at a rated voltage of 12 V) and then delivers currents exceeding the rated power output, whereby a higher ripple voltage is also generated. Therefore, this condition must be considered in the invention in order to rule out imperfect error detection.
Furthermore, it is also preferred that a disconnection in the charge line in the presence of the aforementioned condition be detected only when the excitation in the exciting coil is less than 100%. This condition is based on the knowledge that in the case of a disconnection of the charge line from the view of the generator or the Regenerator regulator the same state prevails, at first, as in the case of no request-for current from the electric system with an intact charge line. This state can occur in the error-free case, if, for example, the battery is sufficiently charged and only a few loads are turned on. In this state the generator regulator switches the on period of the output stage of the exciting coils automatically to a minimum (so-called test pulse width).
Since the ripple content or the ripple voltage depends in particular on the generator speed and the current that is delivered, the ripple threshold, which is adapted preferably as a variable to these actuating variables, is predetermined. The simplest possible adaptation of this ripple threshold takes place by means of the following further development of the invention. Before the generator output voltage has reached or exceeded the predetermined load shedding threshold, a sliding mean value of the ripple voltage is preferably formed continuously. Then, even when the charge line is not intact, the result is a residual ripple, since the battery cannot smooth 100% the rectified three phase voltage of the generator. The respective ripple threshold value is then the momentarily applicable mean value of the ripple voltage at the time the generator output voltage reaches or exceeds the load shedding threshold value.
The process of the invention is integrated preferably as an expansion of the software into a generator regulator, which exists in any event, or into a generator controller, which exists in any event.
The invention enables a highly accurate, qualified error detection.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.